It is well known that many skiers enjoy high speeds and jumping motions while traveling down the slope. High speeds refer to the greater and greater velocities which skiers attempt in navigating the slope successfully (and sometimes unsuccessfully). The jumping motions, on the other hand, include movements which loft the skier into the air. Generally, the greater the skier's speed, the higher the skier's loft into the air.
The interest in high speed skiing is apparent simply by observing the velocity of skiers descending the mountain. The interest in the loft motion is less apparent; although it is known that certain enthusiastic snowboarders regularly exclaim “let's catch some air” and other assorted remarks when referring to the amount and altitude of the lofting motion.
The sensations of speed and jumping are also readily achieved in other sporting activities, such as in mountain biking, skating, roller-blading, windsurfing, and skate-boarding. Many mountain bikers and roller-bladers, like the aforementioned skiers, also crave greater speeds and “air” time.
However, persons in such sporting activities only have a qualitative sense as to speed and loft or “air” time. For example, a typical snowboarder might regularly exclaim after a jump that she “caught” some “big sky,” “big air” or “phat air” without ever quantitatively knowing how much time really elapsed in the air.
Speed or velocity also remain unquantified. Generally, a person such as a skier can only assess whether they went “fast”, “slow” or “'average”, based on their perception of motion and speed (which can be grossly different from actual speed such as measured with a speedometer or radar gun).
There are also other factors that sport persons sometimes assess qualitatively. For example, suppose a snowboarder skis a double-diamond ski slope while a friend skis a green, easy slope. When they both reach the bottom, the “double-diamond” snowboarder will have expended more energy than the other, generally, and will have worked up a sweat; while the “green” snowboarder will have had a relatively inactive ride down the slope. Currently, they cannot quantitatively compare how rough their journeys were relative to one another.